The present invention is related generally to ink jet printing and, more particularly, to improving the waterfastness of the printed ink.
Ink jet color printers commonly have four separate color pens, or cartridges: cyan, yellow, magenta, and black, for providing a full gamut of colors and hues. Such ink jet color printers are commonly called xe2x80x9cfour penxe2x80x9d printers.
Porous media has been shown to give instant dry time printing with an ink jet printer. However, print quality, as evidenced by waterfastness, for example, may be compromised by improving other qualities, such as dry time.
With an increased demand for outdoor signage and window displays, efforts have been made to increase the durability of ink jet print by printing pH-sensitive pigmented inks on porous media provided with a coating. The coating typically comprises a bottom coating of silica and a top coating of alumina; see, e.g., U.S. patent application Ser. No. 09/491,642, filed Jan. 27, 2000. Adjusting the pH in the coating helps to immobilize the pH-sensitive pigmented inks, resulting in better waterfastness. However, adjusting the pH in the coating is sometimes not desirable, due to flocculation of the inorganic filler used in the coating fluid at desired pH or image quality (IQ) tradeoff due to flocculation of the pH-sensitive pigmented ink. Also, for media which are not designed to work with certain ink sets, durability is impossible to be achieved without post processing, e.g., lamination.
Thus, there is a need for improved waterfastness on printed porous media without the need for post processing.
In accordance with the present invention, a clear liquid is applied to the print via a fifth pen, thereby fixing the colorants, which in turn improves the durability of the printed ink. The clear fixer fluid comprises at least one organic acid and, optionally, a salt of at least one polymeric acid.
Also in accordance with the invention, a method is provided for fixing a printed ink printed by an ink jet printer, the printed ink comprising an ink composition that would precipitate or flocculate at a pH of about 6 or less. The method comprises:
(a) printing at least one ink on a print medium, the ink(s) containing a pigment to form a pigment-based ink; and
(b) overprinting the ink with the clear fixer fluid.
The clear fixer fluid enhances the wet rub durability, smearfastness, and waterfastness of pigmented ink printed on porous and/or semi-porous alumina- or silica-coated print media.